The present disclosure relates to a method for coating a workpiece consisting of two different metallic materials, a pole tube having two pole tube sections consisting of different materials, and a device for carrying out the method.
Switching or proportional magnets of hydraulic magnetic valves usually have a pole tube with an armature space for accommodating a magnetic armature whose armature plunger penetrates a pole base via which it is possible to adjust a valve slide of the magnetic valve. Since the design of the pole tubes is known from the prior art, for example, from DE 199 52 800 A1, it will not be described in detail here.
The pole tube consists of a material mix, usually of rust-resistant and acid-resistant stainless steel and unalloyed steel, for example construction steel St35 or St37. In order to avoid corrosion of the regions of the pole tube which are not rust-resistant, it is customary to provide the latter with a galvanically applied zinc layer. This coating of the pole tube encounters problems in practice because of the different materials, since the latter behave in a fundamentally different fashion during the pretreatments (degreasing, activation etc.) normally carried out in galvanic processes. Thus, for example, it can happen during the pretreatment that the pole tube regions consisting of stainless steel are polarized differently to those regions which consist of construction steel—and said different polarization then leads to problems in the adhesion of the zinc layer applied later. These adhesion problems can then lead to flaking owing to spalling of the zinc layer in the region of the stainless steel. In order to avoid this, use is made of specifically tuned pretreatment methods which, on the one hand, require a substantial processing outlay and, on the other hand, cannot fully eliminate the adhesion problems outlined.
By contrast, it is the object of the disclosure to provide a method for coating a workpiece consisting of two different metallic materials, a pole tube having two pole tube sections consisting of two different materials, and a device for carrying out the method, by means of which method, pole tube and device an improved adhesion of a corrosion-resistant layer is ensured.
This object is achieved with regard to the method by described herein, with regard to the pole tube described herein and with regard to the device described herein.